Cephalosporin cleavage process

ABSTRACT

A 7-(amic acid) cephalosporin is cleaved by conversion to the corresponding mixed anhydride and cleavage of the mixed anhydride to the corresponding 7-aminocephalosporin or to a corresponding 7-acylamidocephalosporin.

This is a division of application Ser. No. 371,011 filed June 18, 1973,now U.S. Pat. No. 3,905,966.

BACKGROUND OF THE INVENTION

This invention relates to a process for selectively cleaving an amicacid function from a 7-(amic acid) cephalosporin.

It has been a customary practice for some time in the development ofcephalosporin antibiotics to employ an imide substituent in the7-position when that portion of the molecule was not the point ofinvestigation. The presence of such a protective group, particularly thephthalimido group, tended to render the 7-position chemically quiteinert and afforded the possibility to treat other portions of themolecule rather vigorously with the relative assurance that the7-position would remain intact.

However, it has long been recognized that the presence of an imidefunction in the 7-position of a cephalosporin rendered the structureantibiotically only minimally active. Unfortunately, it has beenimpossible to successfully cleave a 7-imido group from a cephalosporinto liberate the protected amino group. Thus, the investigator was leftwith a stable substituent in the 7-position, and one which rendered acephalosporin exhibiting only minimal antibiotic activity. The use ofsuch a substituent thus could be attractive commercially only if itcould conveniently be removed at any desired point in a syntheticscheme.

It is not intended by the above to say, in general, that it has beenimpossible successfully to cleave an imide group. Several methods foraccomplishing this are recognized. The Japanese publication by MinoruShindo, "Cleavage Reactions of the Phthalimido Group", Yuki Gosei KagakuKyokai Shi, 29 (5), (1971) pp. 496-509, contains an extensive discussionof cleavage techniques. Any of these would be available in achievingcleavage of the imide function from a cephalosporin were this the onlyessential consideration. However, it is at least of equal importance toemploy conditions which will accomplish cleavage without sacrificing thestructural integrity of the cephalosporin molecule. To date, this hasbeen impossible to achieve.

It has been possible to achieve a partial cleavage of the imide sidechain of a cephalosporin structure to form the corresponding amic acidside chain (see, for example, Sheehan et al., Journal of the AmericanChemical Society, 73, (1951) pp. 4367-4372; Sheehan et al., Journal ofthe American Chemical Society, 78, (1956) pp. 3680-3683; Perron et al.,Journal of Organic Chemistry, 7, (1964) pp. 483-487). The phthalimidefunction has been converted to the corresponding phthalamic acid byalkaline hydrolysis such as is described in the first Sheehanpublication. However, as noted in the second Sheehan publication, allattempts to carry the cleavage beyond this point have met with failure,the β-lactam ring of the penicillin being preferentially opened withdestruction of the penicillin.

Sheehan, U.S. Pat. No. 3,487,074, discloses the cleavage of6-phthalimido-3-penamyl-carboxylic acid by treatment thereof withhydrazine hydrate in dioxane for 12 hours at room temperature. However,this method has been found to be unsuccessful when applied topenicillins and cephalosporins, although moderate success wasexperienced when this approach was applied to a 7-phthalimido Δ²-cephalosporin [see Spry, D. O., Journal of the American ChemicalSociety, 92, (1970), p. 5007].

A method has now been discovered by which an amic acid function of acephalosporin can be cleaved without opening the β-lactam ring. Thisinvention comprises such a method. Normally, the amic acid function willbe obtained by partial cleavage of an imide function; however, this isby no means essential.

SUMMARY OF THE INVENTION

A process for cleaving the amic acid function of a 7-(amic acid)cephalosporin having the formula ##STR1## in which R and R_(a) arehydrogen, or R and R_(a) taken together with the carbon atoms to whichthey are attached represent an ortho-phenylene ring;

R₁ is a carboxy protecting group; and

R₂ is hydrogen, acetoxy, methoxy, methylthio,(5-methyl-1,3,4-thiadiazol-2-yl)thio, or(1-methyl-1H-tetrazol-5-yl)thio; which comprises

1. reacting said 7-(amic acid) cephalosporin with an alkyl chloroformatein the presence of a tertiary amine to form the corresponding mixedanhydride having the formula ##STR2## in which R_(b) is an alkyl grouphaving from 1 to 4 carbon atoms;

2. reacting the product mixture from the aforementioned chloroformatetreatment with a hydrazine of the formula

    R.sub.3 HNNHR.sub.4

in which R₃ and R₄ independently are hydrogen or methyl; and

3.

a. reacting the reaction mixture from the aforementioned hydrazinetreatment with an acyl halide to produce the corresponding 7-acylamidocephalosporin; or

b. when at least one of R₃ and R₄ is methyl, recovering thecorresponding 7-amino cephalosporin from the reaction mixture of theaforementioned hydrazine treatment; or

c. when R₃ and R₄ are hydrogen, heating the reaction mixture from theaforementioned hydrazine treatment to a temperature of from about 50° C.to about 100° C. to produce the corresponding 7-amino cephalosporin; or

d. when R₃ and R₄ are hydrogen, reacting the reaction mixture from theaforementioned hydrazine treatment with acid to produce thecorresponding 7-amino cephalosporin in the form of its acid additionsalt.

DETAILED DESCRIPTION OF THE INVENTION

Unless otherwise specifically mentioned, as used herein, the terms"cleavage", "cleaving", and the like, are intended to refer to theremoval of a substituent in the 7-position of a cephalosporin thereby toproduce a free 7-amino cephalosporin, a free 7-amino cephalosporin inthe form of its acid addition salt, or a 7-amino cephalosporin resultingfrom removal of the amic acid function followed by re-acylation tocontain another acyl substituent in its 7-position.

In accordance with one aspect of the process of this invention, a firststep involves conversion of an amic acid function to produce acorresponding mixed anhydride. When, in the amic acid structure, R andR_(a) taken together with the carbon atoms to which they are attachedrepresent an ortho phenylene ring, the source of the amic acid generallywill be a phthalimido compound which has been partially cleaved byrecognized techniques. The structure of the resulting phthalamic acid isas follows: ##STR3## The preparation of a compound having the abovestructure from the corresponding phthalimido compound is well-recognizedin the art, and any of the known conditions can be employed. A typicalmethod by which partial cleavage is effected involves an alkalinehydrolysis such as is described in Sheehan et al., Journal of theAmerican Chemical Society, 73, (1951), pp. 4367-4372.

The conditions of alkaline hydrolysis which can be employed toaccomplish partial cleavage to the amic acid include use of an alkalimetal hydroxide or sulfide, such as sodium hydroxide, potassiumhydroxide, lithium hydroxide, sodium sulfide, potassium sulfide, lithiumsulfide, and the like. Generally, from about 1 to about 2 equivalents ofthe alkali metal hydroxide or sulfide are employed, except in theinstance in which the free acid of the cephalosporin is employed, inwhich case the free carboxyl itself will consume one equivalent of thealkaline reagent, and, therefore, an additional equivalent will berequired.

In general, the pH of the reaction medium ranges from about 9 to about11. The hydrolysis is achieved generally by use of an aqueous mediumcontaining an inert, water-miscible organic solvent, such as, forexample, tetrahydrofuran, N,N-dimethylformamide, acetone,dimethylsulfoxide, dioxane, and the like.

The partial cleavage generally is quite rapid, typically being completedin from about 3 to about 30 minutes, and more typically in from about 5to about 10 minutes. The temperature of reaction usually is from about-10° C. to about room temperature, and preferably, about 0° C.

The amic acid can also have the formula ##STR4## The above amic acid, aswell as phthalamic acid defined herein, are also available from sourcesother than their corresponding imide precursors. For example, the freeamino compound can be reacted with the appropriate anhydride, forexample, maleic anhydride, to produce the corresponding amic acidcompound, specifically, in this case, the 3-carboxyacrylamido compound.

One step of the process of this invention comprises the conversion ofthe amic acid to a mixed anhydride. The mixed anhydride is not isolatedin accordance with the process of this invention; however, it has theformula ##STR5##

R_(b) represents an alkyl group, preferably a lower alkyl group havingfrom 1 to 4 carbon atoms.

The conversion of the amic acid to the mixed anhydride is accomplishedby reacting the amic acid with an alkyl chloroformate, such as ethylchloroformate, propyl chloroformate, t-butyl chloroformate, isobutylchloroformate, and the like. Preferably, a lower alkyl chloroformate isemployed, typically one in which the alkyl group has from about 1 toabout 4 carbon atoms. This reaction is carried out in the presence of atertiary amine, such as pyridine, quinoline, triethylamine,N-methylmorpholine, N,N-dimethylaniline, and the like. Additionally,this reaction typically is carried out in the presence of an aproticorganic solvent, that is, one which does not offer or accept protons. Awide variety of such solvents are known to those skilled in the art andcan be used in accordance with the process of this invention. Includedas such solvents are N,N-dimethylformamide, N,N-dimethylacetamide,tetrahydrofuran, dioxane, aliphatic nitriles, such as acetonitrile,propionitrile, and the like; aromatic hydrocarbons and halogenatedderivatives, such as benzene, toluene, dichlorobenzene, and the like;and aliphatic halogenated hydrocarbons, such as methylene chloride,chloroform, bromoform, carbon tetrachloride, carbon tetrabromide,ethylene dichloride, ethylene dibromide, and the like.

No more than one equivalent of the amine based upon the amic acid isemployed, and it is highly preferred to employ a slightly deficientquantity of the amine. Any excess tertiary amine will tend to convertthe amic acid to an imide, typically what may have been the originalstarting material in the process of this invention. A slight excess ofthe chloroformate can be employed; however, this is not preferred, sinceany excess will react with the hydrazine employed in the next step ofthe process of this invention.

The reaction is carried out for from about 5 to about 40 minutes,preferably from about 20 to about 30 minutes at a temperature of fromabout -20° C. to about +5° C., and preferably from about -20° C. toabout -5° C. The mixed anhydride is maintained intact by retaining thereaction mixture at approximately the temperature at which the reactionwas carried out.

The aforementioned mixed anhydride cephalosporin can then be selectivelycleaved by a step-wise treatment thereof with a hydrazine, typicallyunsubstituted hydrazine, methyl hydrazine, or N,N'-dimethylhydrazine,followed by product recovery and/or further treatment depending upon theproduct which is desired and the particular hydrazine which is employed.

The hydrazine treatment involves the reaction of the mixed anhydride inan inert organic solvent such as any of the aprotic solvents mentionedhereinabove with one equivalent of the hydrazine. Care must be taken toavoid the presence of any excess hydrazine. Therefore, in order toensure the avoidance of such excess, up to one equivalent of thehydrazine per equivalent of the original amic acid is employed, and,typically, a slight deficiency of hydrazine is employed. The reaction iscarried out at relatively cold temperatures ranging from about -10° C.to about room temperature and preferably at about ice temperature (0°C.). The hydrazine typically is added to the mixed anhydride mixturewhile the mixture is at the relatively cold reaction temperature. Thus,the mixture of the mixed anhydride in the organic solvent is maintainedat the temperature of reaction while the hydrazine, previously cooled,is added. The reaction is rather rapid, generally being completed withinfrom about 1 to about 10 minutes, and the reaction generally ispermitted to proceed for about an additional 5 minutes.

The particular treatment which the hydrazine reaction mixture thenreceives depends upon the structure of the hydrazine which is employedand the ultimate product which is desired.

The hydrazines which are used have the structure

    R.sub.3 HNNHR.sub.4

in which R₃ and R₄ independently are hydrogen or methyl. When either orboth of R₃ and R₄ are methyl, no further treatment is necessary sincethe free 7-amino cephalosporin is generated and can be isolated simplyby applying techniques well recognized in the art.

When R₃ and R₄ in the hydrazine which is employed are both hydrogen, acomplex of the free 7-amino cephalosporin and the by-product,diketophthalazine, forms, and this complex must be broken. This can beaccomplished by heating the mixture or by treating the mixture with acidor, more readily, by a combination of both heat and acid treatment.

When heat is employed, the complex typically can be broken by subjectingthe reaction mixture to a temperature of from about 50° C. to about 100°C. for from about 5 to about 20 minutes, and the free amino compoundrecovered by recognized techniques.

The diketophthalazine complex can also be broken by treating thereaction mixture with an acid. Virtually any acid, organic or inorganic,can be used. Typical such acids include, for example, hydrochloric acid,hydrobromic acid, phosphoric acid, p-toluenesulfonic acid, sulfuricacid, methanesulfonic acid, and the like. An equivalent or a moderateexcess of the acid, typically up to about two equivalents of the acid,based upon the amic acid, is employed. Preferably, acid is employed inconjunction with heat, and, therefore, the resulting reaction mixture isheated to a temperature of from about 50° C. to about 100° C., and thedecomposition of the complex is permitted to proceed. Depending upon therelative temperature which is employed, the reaction typically will becompleted within from about 5 to about 10 minutes. When an acid isemployed, the free 7-amino cephalosporin in the form of its acidaddition salt is thereby produced and is recovered in accordance withknown techniques.

It is also possible to form a 7-acylamido cephalosporin by subjectingthe hydrazine reaction mixture to treatment with an acyl halide whichcontains an acyl function which, in combination with the 7-aminocephalosporin, will form the desired acylamido function. The use of anacyl halide obviates any necessity for heat or acid treatment todecompose the diketophthalazine complex, should such have formed, sincethe acyl halide itself is sufficiently acidic to accomplish thenecessary decomposition. Any of the typical acyl functions can bethereby introduced into the 7-position of the cephalosporin moleculesimply by selection of the appropriate acyl halide, preferably thecorresponding acyl chloride. The resulting 7-acylamido cephalosporin canbe readily recovered by techniques well recognized in the art.

Typical acyl halides, each of which can be employed to produce theultimate 7-acylamido product, are those of the formula

    R.sub.x -Y

in which Y is a halogen, such as chlorine, bromine, or iodine, and R_(x)is C₁ to C₈ -alkanoyl; C₂ to C₈ -chloro- or bromoalkanoyl; azidoacetyl;cyanoacetyl; 2-sydnone-3-C₁ to C₃ -alkanoyl; ##STR6## in which m iszero, 1, or 2; ##STR7##

in which each Q is hydrogen or methyl, and Ar is 2-thienyl, 3-thienyl,2-furyl, 3-furyl, 2-pyrrolyl, 3-pyrrolyl, phenyl, or phenyl substitutedwith chlorine, bromine, iodine, fluorine, trifluoromethyl, hydroxy, C₁to C₃ -alkyl, C₁ to C₃ -alkyloxy, cyano, or nitro;

Ar--X--CH₂ --C(O)-- in which X is oxygen or sulfur, and Ar is as definedabove; or Ar is 4-pyridyl and X is sulfur; or ##STR8## in which Ar is asdefined above, and B is --NH₂ ; an amino group protected withbenzyloxycarbonyl, C₁ to C₄ -alkoxycarbonyl, cyclopentyloxycarbonyl,cyclohexyloxycarbonyl, benzhydryloxycarbonyl, triphenylmethyl,2,2,2-trichloroethoxycarbonyl, ##STR9## or the enamine from methylacetoacetate or acetylacetone; --OH, or --OH protected by esterificationwith a C₁ to C₆ -alkanoic acid; --COOH, or --COOH protected byesterification with a C₁ to C₆ -alkanol; --N₃ ; --CN; or --C(O)NH₂.

The cephalosporin used as starting material in the process of thisinvention has the following formula: ##STR10##

R₁ in the above formula as well as in the various products of theprocess of this invention denotes a carboxy protecting group. The natureof the carboxy protecting group is not important, and any of thoserecognized in the art can be used. Preferably, however, this group isthe residue of an ester function which is removable by acid treatment orby hydrogenation. Preferred carboxy protecting groups include, forexample, C₁ -C₄ alkyl, 2,2,2-trihaloethyl, benzyl, p-nitrobenzyl,p-methoxybenzyl, benzhydryl, C₂ to C₆ -alkanoyloxymethyl, phenacyl, orp-halophenacyl, in any of the above of which halo denotes chlorine,bromine, or iodine. Specific illustrations of the preferred esterresidues of the carboxyl group of the 7-imido cephalosporin compoundused in the process of this invention include, for example, methyl,ethyl, n-propyl, isopropyl, n-butyl, sec-butyl, isobutyl, t-butyl,2,2,2-trichloroethyl, 2,2,2-tribromoethyl, p-nitrobenzyl, benzyl,p-methoxybenzyl, benzhydryl, acetoxymethyl, pivaloyloxymethyl,propionoxymethyl, phenacyl, p-chlorophenacyl, p-bromophenacyl, and thelike.

Highly preferred ester residues are t-butyl, benzyl, p-nitrobenzyl,p-methoxybenzyl, benzhydryl, and 2,2,2-trichloroethyl; most preferably,the ester residue is p-nitrobenzyl.

In the above formula, the 7-position of the cephalosporin contains a2-carboxybenzamido group (typically derived from a phthalimido group) ora maleamido group.

Thus, the process of this invention proceeds step-wise from a7-(2-carboxybenzamido)- to an unisolated mixed anhydride to a 7-amino-or 7-acylamido- cephalosporin.

It is also possible to begin the process of this invention with amaleamido cephalosporin. This step-wise sequence includes conversion of7-maleamido- to an unisolated mixed anhydride to a 7-amino- or7-acylamido- cephalosporin.

The nature of the substituent in the 3-position of the 7-imido or7-(amic acid) cephalosporin starting material is not critical, and anyof the recognized substituents can be present. Preferably, however, the3-position will contain one of the following: methyl, acetoxymethyl,methoxymethyl, methylthiomethyl,(5-methyl-1,3,4-thiadiazol-2-yl)thiomethyl, or(1-methyl-1H-tetrazol-5-yl)thiomethyl. The substituent which is presentin the 3-position of the cephalosporin starting material will remainintact throughout the sequence of the process of this invention.

The following are representative of the product conversions which areavailable in accordance with the process of this invention. It will beunderstood, however, that the ratio of products may vary depending uponthe particular reactants which are employed, the relative quantities ofreactants, and the conditions of reaction.

Methyl 7-(2-carboxybenzamido)-3-methyl-3-cephem-4-carboxylate to methyl7-amino-3methyl-3-cephem-4-carboxylate.

2,2,2-Trichloroethyl7-(2-carboxybenzamido)-3-acetoxymethyl-3-cephem-4-carboxylate to2,2,2-trichloroethyl 7-amino-3-acetoxymethyl-3cephem-4-carboxylate.

p-Nitrobenzyl7-(2-carboxybenzamido)-3-methoxymethyl-3-cephem-4-carboxylate top-nitrobenzyl 7-amino-3-methoxymethyl-3-cephem-4-carboxylate.

Benzyl 7-(2-carboxybenzamido)-3-methylthiomethyl-3-cephem-4-carboxylateto benzyl 7-amino-3-methylthiomethyl-3-cephem-4-carboxylate.

Benzhydryl7-(2-carboxybenzamido)-3-(5-methyl-1,3,4-thiadiazol-2-yl)thiomethyl-3-cephem-4-carboxylateto benzhydryl7-amino-3-(5-methyl-1,3,4-thiadiazol-2-yl)thiomethyl-3-cephem-4-carboxylate.

t-Butyl7-(2-carboxybenzamido)-3-(1-methyl-1H-tetrazol-5-yl)thiomethyl-3-cephem-4-carboxylateto t-butyl7-amino-3-(1-methyl-1H-tetrazol-5-yl)thiomethyl-3-cephem-4-carboxylate.

p-Nitrobenzyl7-(2-carboxybenzamido)-3-acetoxymethyl-3-cephem-4-carboxylate top-nitrobenzyl 7-amino-3-acetoxymethyl-3-cephem-4-carboxylate.

p-Nitrobenzyl 7-(2-carboxybenzamido)-3-methyl-3-cephem-4-carboxylate top-nitrobenzyl 7-amino-3-methyl-3-cephem-4-carboxylate.

p-Nitrobenzyl7-(2-carboxybenzamido)-3-methylthiomethyl-3-cephem-4-carboxylate top-nitrobenzyl 7-amino-3-methylthiomethyl-3-cephem-4-carboxylate.

p-Nitrobenzyl7-(2-carboxybenzamido)-3-(5-methyl-1,3,4-thiadiazol-2-yl)thiomethyl-3-cephem-4-carboxylateto p-nitrobenzyl7-amino-3-(5-methyl-1,3,4-thiadiazol-2-yl)thiomethyl-3-cephem-4-carboxylate.

p-Nitrobenzyl7-(2-carboxybenzamido)-3-(1-methyl-1H-tetrazol-5-yl)thiomethyl-3-cephem-4-carboxylateto p-nitrobenzyl7-amino-3-(1-methyl-1H-tetrazol-5-yl)thiomethyl-3-cephem-4-carboxylate.

p-Methoxybenzyl7-(2-carboxybenzamido)-3-acetoxymethyl-3-cephem-4-carboxylate top-methoxybenzyl 7-amino-3-acetoxymethyl-3-cephem-4-carboxylate.

p-Nitrobenzyl 7-maleamido-3-methyl-3-cephem-4-carboxylate top-nitrobenzyl 7-amino-3-methyl-3-cephem-4-carboxylate.

2,2,2-Trichloroethyl7-maleamido-3-(1-methyl-1H-tetrazol-5-yl)thiomethyl-3-cephem-4-carboxylateto 2,2,2-trichloroethyl7-amino-3-(1-methyl-1H-tetrazol-5-yl)thiomethyl-3-cephem-4-carboxylate.

Benzyl7-maleamido-3-(5-methyl-1,3,4-thiadiazol-2-yl)thiomethyl-3-cephem-4-carboxylateto benzyl7-amino-3-(5-methyl-1,3,4-thiadiazol-2-yl)thiomethyl-3-cephem-4-carboxylate.

Pivaloyloxymethyl7-(2-carboxybenzamido)-3-methylthiomethyl-3-cephem-4-carboxylate topivaloyloxymethyl 7-amino-3-methylthiomethyl-3-cephem-4-carboxylate.

Acetoxymethyl7-(2-carboxybenzamido)-3-methoxymethyl-3-cephem-4-carboxylate toacetoxymethyl 7-amino-3-methoxymethyl-3-cephem-4-carboxylate.

Phenacyl 7-(2-carboxybenzamido)-3-methyl-3-cephem-4-carboxylate tophenacyl 7-amino-3-methyl-3-cephem-4-carboxylate.

p-Chlorophenacyl7-(2-carboxybenzamido)-3-acetoxymethyl-3-cephem-4-carboxylate top-chlorophenacyl 7-amino-3-acetoxymethyl-3-cephem-4-carboxylate.

t-Butyl 7-(2-carboxybenzamido)-3-methyl-3-cephem-4-carboxylate tot-butyl 7-amino-3-methyl-3-cephem-4-carboxylate.

Benzyl 7-(2-carboxybenzamido)-3-acetoxymethyl-3-cephem-4-carboxylate tobenzyl 7-amino-3-acetoxymethyl-3-cephem-4-carboxylate.

p-Methoxybenzyl7-(2-carboxybenzamido)-3-methoxymethyl-3-cephem-4-carboxylate top-methoxybenzyl 7-amino-3-methoxymethyl-3-cephem-4-carboxylate.

2,2,2-Trichloroethyl7-(2-carboxybenzamido)-3-methylthiomethyl-3-cephem-4-carboxylate to2,2,2-trichloroethyl 7-amino-3-methylthiomethyl-3-cephem-4-carboxylate.

t-Butyl7-(2-carboxybenzamido)-3-(5-methyl-1,3,4-thiadiazol-2-yl)thiomethyl-3-cephem-4-carboxylateto t-butyl7-amino-3-(5-methyl-1,3,4-thiadiazol-2-yl)thiomethyl-3-cephem-4-carboxylate.

Benzyl7-(2-carboxybenzamido)-3-(1-methyl-1H-tetrazol-5-yl)thiomethyl-3-cephem-4-carboxylateto benzyl7-amino-3-(1-methyl-1H-tetrazol-5-yl)thiomethyl-3-cephem-4-carboxylate.

The final product in the immediately preceding list is presented in theform of the free 7-amino compound. However, in accordance with theprocess of this invention, when an acid treatment is employed, it willbe initially obtained in the form of its acid addition salt. This salt,of course, can be readily converted to the free 7-amino compound by wellrecognized techniques.

Furthermore, the process conversions illustrated hereinabove do notreflect another aspect of this invention, namely, the possibility toobtain, instead of the free 7-amino compound or the acid addition saltthereof, a corresponding 7-acylamido compound. This product isobtainable by employing an acyl halide, typically the acyl chloride, ofthe 7-acylamido function intended in the final product. The acyl halideis employed in place of the acid used in the final step of the cleavageprocess. It has been discovered that by so doing the acyl halide itselfis sufficiently acidic to break any intermediate complex which may bepresent in the reaction mixture from the hydrazine treatment.Concomitantly therewith, the free 7-amino group is acylated to thecorresponding 7-acylamido compound.

Any of the well recognized acyl groups can be introduced into the7-position by appropriate selection of the particular acyl halide. Theseinclude, for example, phenylacetyl, phenoxyacetyl, phenylglycyl,2-thienylacetyl, mandelyl, and the like.

Virtually any acyl halide can be employed. Typical such acyl halidesinclude, for example, acetyl chloride, hexanoyl bromide, chloroacetylchloride, γ-bromooctanoyl chloride, azidoacetyl bromide, cyanoacetylchloride, sydnoneacetyl chloride, tetrazolacetyl chloride,2-thienylacetyl chloride, 3-thienylacetyl bromide, 2-furylacetyl iodide,3-furylacetyl chloride, 2-pyrrolylacetyl bromide, 3-pyrrolylacetylchloride, phenylacetyl chloride, α,α-dimethylphenylacetyl chloride,p-chlorophenylacetyl chloride, m-bromophenylacetyl bromide,p-iodophenylacetyl chloride, p-fluorophenylacetyl chloride,m-trifluoromethylphenylacetyl bromide, p-hydroxyphenylacetyl chloride,p-tolylacetyl bromide, m-methoxyphenylacetyl chloride,p-cyanophenylacetyl chloride, p-nitrophenylacetyl bromide, phenoxyacetylchloride, phenylthioacetyl chloride, p-hydroxyphenoxyacetyl bromide,4-pyridylthioacetyl chloride, m-chlorophenoxyacetyl chloride,α-aminophenylacetyl chloride, N-(benzyloxycarbonyl)-α-aminophenylacetylbromide, N-(methoxycarbonyl)-α-aminophenylacetyl chloride,N-(cyclopentyloxycarbonyl)-α-aminophenylacetyl chloride,N-(cyclohexyloxycarbonyl)-α-aminophenylacetyl chloride,N-(benzhydryloxycarbonyl)-α-aminophenylacetyl bromide,N-(triphenylmethyl)-α-aminophenylacetyl chloride,N-(2,2,2-trichloroethoxycarbonyl)-α-aminophenylacetyl chloride,α-hydroxyphenylacetyl chloride, α-formyloxyphenylacetyl chloride,α-acetoxyphenylacetyl chloride, α-carboxyphenylacetyl chloride,α-methoxycarbonylphenylacetyl chloride, α-(t-butoxycarbonyl)phenylacetylchloride, α-azidophenylacetyl chloride, α-cyanophenylacetyl chloride,α-carbamoylphenylacetyl chloride, and the like.

The products produced in accordance with the process of this inventioncan be isolated by employing conventional methods. These can include,for example, chromatographic separation, filtration, recrystallization,and the like.

Since the ultimate product of the process of this invention is an ester,the product can be converted to an active antibiotic by, in addition toappropriate acylation of the 7-amino function, cleavage of the esterfunction by known techniques. Deesterification can be achieved bytreatment of the ester with an acid such as trifluoroacetic acid,hydrochloric acid, and the like, or with zinc and acid, such as formicacid, acetic acid, or hydrochloric acid. It can likewise be accomplishedby hydrogenating the ester in the presence of palladium, rhodium, or acompound thereof, in suspension or on a carrier such as barium sulfate,carbon, alumina, or the like.

The following examples are provided to further illustrate thisinvention. It is not intended that this invention be limited in scope byreason of any of these examples.

Preparation A. Methyl 7-phthalamido-3-methyl-3-cephem-4-carboxylate

To a solution of 17.3 g. (0.05 mol.) of7-phthalimido-3-methyl-3-cephem-4-carboxylic acid in 50 ml. of acetoneand 20 ml. of water, 5 g. (0.05 mol.) of KHCO₃ were slowly added. Theresulting solution was evaporated to dryness, and 38 ml. of DMF and 5ml. of methyl iodide were added to the residue. The mixture was stirredfor 3 hrs. at room temperature. To this mixture were then added 100 g.of ice, and the resulting solid product was filtered. The product wascrystallized from a mixture of 100 ml. of 2-propanol and 100 ml. ofacetone. Yield: 7.91 of crystals, m.p. 187°-188°; ir (CHCl₃) 1790 and1735 cm⁻ ¹, nmr (CDCl₃) δ 2.31 (s, 3, CH₃), 3.0 and 3.75 (ABq, 2, J=15Hz), 3.85 (s, 3, CH₃), 5.15 (d, 1, J=4.4 Hz), 5.74 (d, 1, J=4.4 Hz) and7.73 (m, 4, ArH).

Anal. calcd. for C₁₇ H₁₄ N₂ O₅ S: C, 56.98; H, 3.94; N, 7.82; S, 8.95.Found: C, 56.75; H, 3.66; N, 7.53; S, 8.89%.

Preparation B. t-Butyl 7-phthalimido-3-methyl-3-cephem-4-carboxylate

A mixture of 13.76 g. (40 mmol.) of7-phthalimido-3-methyl-3-cephem-4-carboxylic acid, 10 ml. of conc. H₂SO₄, 100 ml. of dry dioxane and 50 ml. of liquid isobutylene was stirredat room temperature in a sealed pressure bottle and then poured into anexcess of ice cold aqueous NaHCO₃ (44 g.). Extraction of the resultingmixture with ethyl acetate and evaporation of the solvent gave a crudeester which was crystallized from CHCl₃. The first crop gave 3.34 g. ofcrystals, m.p. 189°-191°, and the second crop 1.72 g., m.p. 181°-183°;[α]_(D) = 77.7° (MeCN); ir (CHCl₃) 1800, 1785, and 1735 cm⁻ ¹ ; nmr(CDCl₃) δ 1.55 (s, 9, t-Bu); 2.23 (s, 3, CH₃), 3.05 and 3.6 (ABq, 2, J =16 Hz), 5.1 (d, 1, J = 4.5 Hz), 5.72 (d, 1, J = 4.5 Hz) and 7.8 (m, 4,ArH).

Anal. calcd. for: C₂₀ H₂₀ N₂ O₅ S: C, 59.99; H, 5.03; N, 7.00; O, 19.98;S, 8.01. Found: C, 60.27; H, 4.91; N, 7.04; O, 20.06; S, 7.74%.

Preparation C. t-Butyl7-phthalimido-3-acetoxymethyl-3-cephem-4-carboxylate and t-butyl7-(2-carboxybenzamido)-3-acetoxy-3-cephem-4-carboxylate

A mixture of 3.28 g. (10 mmol.) of t-butyl 7-aminocephalosporanate(7-ACA), 1.5 g. (10 mmol.) of phthalic anhydride and 25 ml. of benzenewas refluxed for 2 hrs. using a Dean-Stark water collector. The solutionwas cooled, washed with NaHCO₃ (1.68 g. in 20 ml. of H₂ O), water, andbrine, and then dried. The solvent was evaporated to give 1.22 g. of aneutral product. The product was chromatographed over silica gel using agradient mixture of benzene and ethyl acetate. Fraction 54-87 gave 330mg. of the phthalimido compound which was recrystallized fromdichloromethane/ether; prisms, m.p. 176°-178°; [α]_(D) + 43.4° (MeCN);ir (CHCl₃) 1800, 1785 and 1735 cm⁻ ¹ ; δEtOH 260 mμ (ε=10,000); nmr(CDCl₃) δ 1.55 (s, 9, t-Bu); 2.1 (s, 3, CH₃), 3.5 (s, 2, CH₂); 4.9 and5.3 (ABq, 2, J = 14 Hz); 5.1 (d, 1, J = 4.5 Hz); 5.82 (d, 1, J = 4.5Hz), and 7.82 (m, 4, ArH).

Anal. calcd. for: C₂₂ H₂₂ N₂ O₇ S: C, 57.63; H, 4.84; N, 6.11; O, 24.43;S, 6.99. Found: C, 57.56; H, 4.60; N, 6.31; O, 24.60; S, 6.90%.

After removal of the neutral product the aqueous portion was acidifiedto pH 3.6 and the acid mixture was extracted with ethyl acetate.Evaporation of the ethyl acetate gave 2.9 g. of t-butyl7-(2-carboxybenzamido) cephalosporanate. This material was dissolved in50 ml. of benzene, 15 mg. of imidazole was added, and the mixture wasrefluxed for 30 min. using a Dean-Stark water collector. After work upprocedure and chromatography, 430 mg. of t-butyl 7-phthalimidocephalosporanate was obtained.

The ratio of products from the condensation of phthalic anhydride andthe t-Bu ester of 7-ACA depends upon the particular reaction time. Ifthe mixture were heated for only 15 min., about 160 mg. of thephthalimido compound and about 4.34 g of the phthalamic acid compoundwould have been obtained.

Preparation D. p-Methoxybenzyl7-phthalimido-3-methyl-3-cephem-4-carboxylate

To a suspension of 13.4 g. (38 mmol.) of7-phthalimido-3-methyl-3-cephem-4-carboxylic acid in 20 ml. of dioxaneand 10 ml. of water were slowly added 3.8 g. of KHCO₃. The solution wasevaporated to dryness, and 100 ml. of DMF and 8.8 g. of p-methoxybenzylbromide were added to the potassium salt residue. The mixture wasstirred for 2 hrs. and then poured onto 200 g. of ice. The resultingmixture was extracted twice with ethyl acetate. The extract was washedwith water and brine, dried, and the solent was then evaporated. Theresidue was recrystallized from ethyl acetate. Yield: 4.1 g. of largecrystals, m.p. 118°-121°; second crop 1.8 g.; ]α]_(D) + 41.2° (MeCN), ir(CHCl₃) 1800, 1785, 1745 and 1735 cm⁻ ¹, nmr (CDCl₃) δ 2.15 (s, 3, CH₃);3.0 and 3.7 (ABq, 2, J = 15 Hz), 3.8 (s, 3, CH₃), 5.11 (d, 1, J = 4.5Hz), 5.28 (s, 2, CH₂), 5.75 (d, 1, J = 4.5 Hz), 6.8-7.8 (m, 8).

Anal. calcd. for: C₂₄ H₂₀ N₂ O₆ S: C, 62.06; H, 4.34; N, 6.03; O, 20.67;S, 6.90. Found: C, 62.15; H, 4.31; N, 6.32; O, 20.88; S, 6.82%.

EXAMPLE 1 Methyl 7-(2-carboxybenzamido)-3-methyl-3-cephem-4-carboxylate

To a solution of 2.86 g. (8 mmol.) of methyl7-phthalimido-3-methyl-3-cephem-4-carboxylate in 80 ml. oftetrahydrofuran at 0° C. were added 2.4 g. (10 mmol.) of Na₂ S.9H₂ O and32 ml. of ice water. After 7 minutes at 0° C., 10 ml. of 1N HCl wereadded to the mixture. The volume was reduced in vacuo to about 40 ml.,and the resulting aqueous solution was washed with ethyl acetate. The pHof the aqueous layer was adjusted to 4.5 with 1N HCl and then wasextracted with ethyl acetate (40 ml.). The ethyl acetate layer waswashed with brine (30 ml.), dried over MgSO₄, and evaporated to give 1.8g. of methyl 7-(2-carboxybenzamido)-3-methyl-3-cephem-4-carboxylate asan amorphous colorless solid. Recrystallization from acetone gave ananalytical sample; m.p. 182°-184.5° (dec.); ir (KBr) 1768, 1630, 1610(shoulder) and 1665 cm⁻ ¹ ; nmr (CDCl₃ /DMSO_(d-6)) 2.08 (s, 3, CH₃),3.12 and 3.52 (ABq, 2, J = 17 Hz), 3.8 (s, 3, CH₃ ester), 5.06 (d, 1,' J= 4.5 Hz), 5.86 (dd, 1, J = 8.0 Hz) and 7.4-8.0δ (m, 4, ArH).

Anal. calcd. for C₁₇ H₁₆ N₂ O₆ S: C, 54.25; H, 4.28; N, 7.44; S, 8.52.Found: C, 53.98; H, 4.18; N, 7.73; S, 8.58.

The pH of the aqueous layer from above was lowered to pH 2.5 with 1N HCland then was extracted with ethyl acetate (2 × 30 ml.). The ethylacetate extracts were combined, washed with brine (30 ml.) and driedover MgSO₄. The ethyl acetate was evaporated in vacuo during which timea colorless crystalline product crystallized. When the volume had beenreduced to ca. 10 ml., the solution was filtered giving 190 mg. (6.5%)of 7-(2-carboxybenzamido)-3-methyl-2-cephem-4-carboxylic acid; m.p.196-198 (dec.); ir (KBr) 1773, 1700, and 1658 cm⁻ ¹ ; nmr (DMSO_(d6))1.88 (s, 3, CH₃), 4.64 (s, 1, C₄ -H), 5.15 (d, 1, J = 4.0 Hz), 5.5 (dd,1, J = 4.0 and 8.0 Hz), 6.15 (s, 1, C₂ -H) and 7.4-8.0δ (m, 4, ArH).

Anal. calcd. for C₁₆ H₁₄ N₂ O₆ S: C, 53.03; H, 3.89; N, 7.73; S, 8.85.Found: C, 52.76; H, 3.85; N, 7.68; S, 8.77.

Evaporation of the filtrate from above gave an additional 600 mg. ofmethyl 7-(2-carboxybenzamido)-3-methyl-3-cephem-4-carboxylate; totalyield--80%.

EXAMPLE 2 Methyl 7-amino-3-methyl-3-cephem-4-carboxylate hydrochloride

To a suspension of methyl7-(2-carboxybenzamido)-3-methyl-3-cephem-4-carboxylate (752 mg., 2mmol.) in 35 ml. of tetrahydrofuran at 0° C. was added triethylamine(0.28 ml., 2 mmol.). After 15 minutes, ethyl chloroformate (0.2 ml., 2mmol.) was added, and then after 1/2 hour at 0° C., anhydrous hydrazine(0.07 ml., 2.2 mmol.) was added to the reaction mixture. After 15minutes, the mixture was filtered, and the filtrate was evaporated invacuo to dryness. The crude product was taken up in 20 ml. ofchloroform, refluxed for 90 minutes, and then allowed to stir at about35° C. overnight. Filtration gave 180 mg. of diketophthalazine (m.p.340°-343°). The filtrate was evaporated to dryness in vacuo. Theresulting crude product was taken up in 3 ml. of 1N HCl plus 2 ml. waterand washed with ethyl acetate (2×7 ml.). Evaporation of the aqueouslayer in vacuo gave a yellow amorphous solid which was recrystallizedfrom ethanol/diethyl ether to give 115 mg. of methyl7-amino-3-methyl-3-cephem-4-carboxylate hydrochloride.

EXAMPLE 3 t-Butyl7-(2-carboxybenzamido)-3-acetoxymethyl-3-cephem-4-carboxylate.

A solution of 458 mg. (1 mmol.) of t-butyl7-phthalimido-3-acetoxymethyl-3-cephem-4-carboxylate in 10 ml. of THFwas cooled in an ice water bath, and 1.1 ml. of 1N NaOH were then added.After stirring for 5 min., 10 ml. of water and 30 ml. of ethyl acetatewere added. The ethyl acetate layer was separated, and 70 mg. ofstarting material were recovered therefrom. The aqueous layer wasacidified to pH 4.0, and the acidified layer was extracted with ethylacetate. After workup, 330 mg. (83%) of the desired phthalamic acid wereobtained [α] + 26.37 (MeCN); .sup.λEtOH 260 mμ (ε 8800)^(D) ; ir (CHCl₃)1785, 1730 and 1685 cm⁻ ¹ ; nmr (CDCl₃) δ 1.55 (s, 9, t-Bu), 2.05 (s, 3,Ac), 3.3 and 3.6 (ABq, 2, J = 17 Hz), 4.72 and 5.2 (ABq, 2, J = 14 Hz),4.98 (d, 1, J = 4.5 Hz), 5.9 (dd, 1, J = 4.5 and 9 Hz), and 7.5-8 (m, 4,ArH).

EXAMPLE 4 t-Butyl 7-amino-3-acetoxymethyl-3-cephem-4-carboxylate

In accordance with the procedure of Example 2, t-butyl7-(2-carboxybenzamido)-3-acetoxymethyl-3-cephem-4-carboxylate isconverted to t-butyl 7-amino-3-acetoxymethyl-3-cephem-4-carboxylatehydrochloride, which is converted to the free amine by treatment withNaHCO₃ and extraction with chloroform. M.p., ir and nmr spectra are inagreement with an authentic sample prepared according to the method ofR. J. Stedman, J. Med. Chem., (1966) p. 444.

EXAMLE 5 t-Butyl 7-(2-carboxybenzamido)-3-methyl-3-cephem-4-carboxylate

A solution of 800 mg. (2 mmol.) of t-butyl7-phthalimido-3-methyl-3-cephem-4-carboxylate in 25 ml. oftetrahydrofuran and 8 ml. of water was cooled in an ice bath. To thesolution 660 mg. of Na₂ S.9H₂ O were added, and the mixture was stirredand cooled for 10 min. At the end of this period 10 ml. of water wereadded, and the mixture was extracted with 40 ml. of ethyl acetate. Theextract was discarded. The aqueous portion was acidified to pH 4.3 with1N H₂ SO₄ and then extracted with ethyl acetate. The ethyl acetateextract was dried and evaporated, giving 700 mg. of the title compound.The product was recrystallized from chloroform/cyclohexane; m.p.178°-179°; ir (nujol) 1770, 1735, and 1680 cm⁻ ¹ ; nmr (CDCl₃ +DMSO_(d6)) δ 1.5 (s, 9, t-Bu), 2.1 (s, 3, CH₃), 3.2 and 3.5 (ABq, 2, J =18 Hz), 5.02 (d, 1, J = 4.5 Hz), 5.82 (dd, 1, J = 4.5 and 9Hz), and7.4-8 (m, H, ArH).

Anal. calcd. for C₂₀ H₂₂ N₂ O₆ S: c, 57.40; H, 5.30; N, 6.69; O, 22.94and S, 7.66. Found: C, 57.70; H, 5.20; N, 6.52; O, 22.72 and S, 7.53%.

The identical (nmr, ir, m.p.) substance also can be obtained in 94%yield from phthalic anhydride and the t-butyl ester of 7-ADCA.

EXAMPLE 6 t-butyl 7-amino-3-methyl-3-cephem-4-carboxylate

In accordance with the procedure of Example 2, t-butyl7-(2-carboxybenzamido)-3-methyl-3-cephem-4-carboxylate is converted tot-butyl 7-amino-3-methyl-3-cephem-4-carboxylate hydrochloride. Thehydrochloride salt is converted to the free amino ester, a colorlesssolid, using ethyl acetate and sodium bicarbonate.

EXAMPLE 7 p-Methoxybenzyl7-(2-carboxybenzamido)-3-methyl-3-cephem-4-carboxylate

A solution of 930 mg. (2 mmol.) of p-methoxybenzyl7-phthalimido-3-methyl-3-cephem-4 -carboxylate in 25 ml. of THF and 8ml. of water was cooled in an ice water bath, and 660 mg. of Na₂ S.9H₂ Owere then added. The mixture was stirred for 15 min., and 10 ml. ofwater and 40 ml. of ethyl acetate were added. The layers were separated,and 140 mg. of a neutral material were obtained from the ethyl acetatelayer. The aqueous layer was acidified to pH 4.3 with 1N H₂ SO₄ andextracted twice with ethyl acetate. The ethyl acetate extract waswashed, dried, and evaporated to give 660 mg. (68%) of the phthalamicacid as an amorphous solid, [α]_(D) + 85.6° (MeCN); ir (CHCl₃), 1781,1740 and 1710 cm⁻ ¹ ; nmr (CDCl₃) δ 2.08 (s, 3, CH₃), 3.1 and 3.43 (ABq,2, J = 17 Hz), 3.79 (s, 3, CH₃), 5.0 (d, 1, J = 4.5 Hz), 5.1 (s, 2,CH₂), 5.8 (dd, 1, J = 4.5 Hz), 6.75-7.6 (m, 8).

Anal. calcd. for C₂₄ H₂₂ N₂ O₇ S: C, 59.74; H, 4.60; N, 5.81; O, 23.21;S, 6.65. Found: C, 59.81; H, 4.32; N, 6.07; O, 23.34; S, 6.51%.

EXAMPLE 8 p-Methoxybenzyl 7-amino-3-methyl-3-cephem-4-carboxylate,p-toluene sulfonic acid salt

In accordance with the procedure of Example 2, p-methoxybenzyl7-(2-carboxybenzamido)-3-methyl-3-cephem-4-carboxylate is converted top-methoxybenzyl 7-amino-3-methyl-3-cephem-4-carboxylate,p-toluenesulfonic acid salt, using p-toluenesulfonic acid monohydrate,instead of hydrochloric acid as in Example 2. This material is identicalwith the salt described by Chauvette et. al., J. Org. Chem., 36, 1265(1971).

EXAMPLE 9 p-Nitrobenzyl7-(2-carboxybenzamido)-3-methyl-3-cephem-4-carboxylate

To an ice cooled solution of 480 mg. (1 mmol.) of p-nitrobenzyl7-phthalimido-3-methyl-3-cephem-4-carboxylate in 25 ml. oftetrahydrofuran and 5 ml. of water were added 340 mg. of sodium sulfide(Na₂ S.9H₂ O). The mixture was stirred at pH 11.5 for 7 min., and 40 ml.of ethyl acetate and 10 ml. of water were added. The layers wereseparated, and the organic layer was washed with 5 ml. of water and 5ml. of brine to give 150 mg. of a neutral material. The aqueous layerwas acidified to pH 4.5 with 1N sulfuric acid, and the resultingemulsion was extracted with 25 ml. of ethyl acetate. The extract waswashed with brine, dried and evaporated to dryness to give 290 mg. ofthe crude product, from which 150 mg. (30%) of pure product wasobtained.

The same compound also can be prepared by the alternate procedure ofrefluxing phthalic anhydride and the p-nitrobenzyl ester of 7-ADCA inacetonitrile for 30 min.

A sample was recrystallized from dioxane/water, and colorless crystalswere obtained melting at 192°-193°; nmr (DMSO-d₆) δ 2.04 (s, 3, CH₃),3.35 and 3.68 (ABq,2, J = 18 Hz), 5.2 (d, 1, J = 4 Hz, H-6), 5.4 (s, 2,CH₂), 5.8 (d, d, 1, J = 4.5 and 9 Hz), 8 (m, 8 ArH).

Anal. calcd. for C₂₃ H₁₉ N₃ O₈ S: C, 55.53; H, 3.85; N, 8.45; O, 25.73;S, 6.45. Found: C, 55.67; H, 3.94; N, 8.49; O, 25.89; S, 6.47%.

The subsequent acidification of the aqueous solution to pH 2.0 followedby ethyl acetate extraction produced 120 mg. of p-nitrobenzyl7-(2-carboxybenzamido)-3-methyl-2-cephem-4-carboxylate.

EXAMPLE 10 p-Nitrobenzyl 7-amino-3-methyl-3-cephem-4-carboxylate,p-toluene sulfonate salt

A solution of 1.0 g. (2 mmol.) of p-nitrobenzyl7-(2-carboxybenzamido)-3-methyl-3-cephem-4-carboxylate in 30 ml. of drytetrahydrofuran was cooled in an ice-salt bath, and 0.28 ml. (2 mmol.)of triethylamine and 0.20 ml. (2 mmol.) of ethyl chloroformate wereadded. After cooling and stirring for 20 min., 0.15 ml. of 85% hydrazinehydrate was added, and stirring was continued for 10 min. The Et₃ N.HClsalt was filtered, and the filtrate was evaporated to dryness. Theresidue was dissolved in a mixture of 25 ml. of ethyl acetate and 10 ml.of water. The organic extract was separated from the aqueous and washedwith NaHCO₃ solution, water and brine. After drying, the solvent wasevaporated. The residue was dissolved in 10 ml. of acetonitrile, and thesolution was refluxed for 50 min. and then cooled. To this solution 380mg. of p-toluenesulfonic acid hydrate and 2.5 ml. of water were added,the precipitate (160 mg.) was filtered, and most of the acetonitrile wasevaporated from the filtrate. Upon cooling and scratching,crystallization began. Two hours later 680 mg. (63%) of the titlecompound were collected. The purity of product was tested by thin-layerchromatography (tlc) using silica plate and MeoH:Benzene (1:3) system. Asample was recrystallized from methanol-ether, m.p. 170°-174° dec., nmr(DMSO₃₋₆) δ 2.20 (s,3,CH₃), 2.30 (s,3,CH₃), 3.6 (s, 2,SCH₂), 5.22(s,2,CH₂ ester), 5.4 (s,2,azetidinone H's), and 7.1-8.25 (m,8 ArH's); ir(KBr) 1780 (azetidinone CO) and 1730 cm⁻ ¹ ester CO).

Anal. calcd for: C₂₂ H₂₃ N₃ O₈ S₂ : C, 50.66; H, 4.45; N, 8.06; S,12.30. Found: C, 51.03; H, 4.27; N, 8.19; S, 11.91%.

EXAMPLE 11 p-Nitrobenzyl7-phenylacetamido-3-methyl-3-cephem-4-carboxylate

To a suspension of p-nitrobenzyl7-(2-carboxybenzamido)-3-methyl-3-cephem-4-carboxylate (462 mg., 1mmol.) in tetrahydrofuran at 0° C. is added triethylamine (0.14 ml., 1mmol.). After 15 minutes, ethyl chloroformate (0.1 ml., 2 mmol.) isadded, and then after 0.5 hour at 0° C., anhydrous hydrazine (0.03 ml.,1 mmol.) is added to the reaction mixture. After 15 minutes, the mixtureis filtered, and the filtrate is evaporated to dryness in vacuo. Theresidue is taken up in acetone (15 ml.) and tetrahydrofuran (15 ml.),and phenylacetyl chloride (0.13 ml., 1 mmol.) is added. After refluxingfor 30 min., the mixture is cooled and evaporated in vacuo to dryness.The product is taken up in chloroform (50 ml.) and washed successivelywith 1N HCl (30 ml.), 10% sodium bicarbonate (40 ml.), and brine (40ml.), dried over MgSO₄, and evaporated in vacuo to dryness. Thecolorless product is slurried with ethyl acetate (12 ml.). Filtrationgives p-nitrobenzyl 7-phenylacetamido-3-methyl-3-cephem-4-carboxylate.Recrystallization from ethyl acetate gives an analytical sample: m.p.227°-230°.

EXAMPLE 12 t-Butyl7-(2'-carboxy)acrylamido-3-acetoxymethyl-3-cephem-4-carboxylate

A solution of 656 mg. (2 mmol.) of t-butyl7-amino-3-acetoxymethyl-3-cephem-4 -carboxylate and 196 mg. (2 mmol.) ofmaleic anhydride in 20 ml. benzene was refluxed for 1/2 hour, cooled,and evaporated in vacuo to dryness. Tlc indicated no starting materialand one slow moving product: nmr (CDCl₃) 94 (s, 9, t-Bu), 127 (s, 3,OAc), 207 and 216 (ABq, 2, J=20 Hz), 293 and 307 (ABq, J=14.0, CH₂ OAc);305 (1, d, J=4.5, azetidinone H), 350 (1, q, J=4.5 and 8.0 Hz,azetidinone H), 390 (2H, q, J=12 and 2.0 Hz), 534 (1, d, J=8.0, NH), and806 Hz (1, broad s, COOH).

EXAMPLE 13 t-Butyl 7-amino-3-acetoxymethyl-3-cephem-4-carboxylate

In accordance with the procedure of Example 2, t-butyl7-(3'-carboxy)acrylamido-3-acetoxymethyl-3-cephem-4-carboxylate isconverted to t-butyl 7-amino-3-acetoxymethyl-3-cephem-4-carboxylatehydrochloride. The hydrochloride-containing reaction mixture is treatedwith ethyl acetate and NaHCO₃ to obtain a tan colored amorphous product.Nmr and tlc data shows the product to be identical to authentic t-butyl7-amino-3-acetoxymethyl-3-cephem-4-carboxylate.

EXAMPLE 14 Benzhydryl7-(2-carboxybenzamido)-3-(5-methyl-1,3,4-thiadiazol-2-yl)thiomethyl-3-cephem-4-carboxylate

A solution of benzhydryl7-phthalimido-3-(5-methyl-1,3,4-thiadiazol-2-yl)thiomethyl-3-cephem-4-carboxylate(2 mmol.) in 25 ml. of THF and 8 ml. of water is cooled in an ice-waterbath, and 660 mg. of Na₂ S.9H₂ O are then added. The mixture is stirredfor 15 minutes, and 10 ml. of water and 40 ml. of ethyl acetate areadded. The layers are separated, and a neutral material is obtained fromthe ethyl acetate layer. The aqueous layer is acidified to pH 4.3 with1N sulfuric acid and is extracted twice with ethyl acetate. The ethylacetate extract is washed, dried, and evaporated to give the titlecompound.

EXAMPLE 15 Benzhydryl7-amino-3-(5-methyl-1,3,4-thiadiazol-2-yl)-thiomethyl-3-cephem-4-carboxylate

A solution of benzhydryl7-(2-carboxybenzamido)-3-(5-methyl-1,3,4-thiadiazol-2-yl)thiomethyl-3-cephem-4-carboxylate(2 mmol.) in 30 ml. of dry tetrahydrofuran is cooled in an ice-saltbath, and 0.28 ml. (2 mmol.) of triethylamine and 0.20 ml. (2 mmol.) ofethyl chloroformate are added. After cooling and stirring for 20minutes, 0.106 ml. (2 mmol.) of N-methylhydrazine in 5 ml. oftetrahydrofuran is added. Stirring is continued for about 10 minutes.The Et₃ N.HCl salt is filtered, and the filtrate is evaporated todryness. The residue is taken up in about 15 ml. of chloroform, and themixture is allowed to stand at room temperature for about one hourduring which time methylphthalhydrazide (m.p. 243°-245° C.)precipitates. Filtration and evaporation in vacuo of the filtrate givescrude benzhydryl7-amino-3-(5-methyl-1,3,4-thiadiazol-2-yl)thiomethyl-3-cephem-4-carboxylate.

EXAMPLE 16 2,2,2-Trichloroethyl7-(2-carboxybenzamido)-3-(1-methyl-1H-tetrazol-5-yl)thiomethyl-3-cephem-4-carboxylate

In accordance with the procedure of Example 14, 2,2,2-trichloroethyl7-phthalimido-3-(1-methyl-1H-tetrazol-5-yl)thiomethyl-3-cephem-4-carboxylateis converted to 2,2,2-trichloroethyl7-(2-carboxybenzamido)-3-(1-methyl-1H-tetrazol-5-yl)thiomethyl-3-cephem-4-carboxylate.

EXAMPLE 17 2,2,2-Trichloroethyl7-amino-3-(1-methyl-1H-tetrazol-5-yl)-thiomethyl-3-cephem-4-carboxylate

In accordance with the procedure of Example 15, 2,2,2-trichloroethyl7-(2-carboxybenzamido)-3-(1-methyl-1H-tetrazol-5-yl)thiomethyl-3-cephem-4-carboxylateis converted to 2,2,2-trichloroethyl7-amino-3-(1-methyl-1H-tetrazol-5-yl)-thiomethyl-3-cephem-4-carboxylatewith the exception that N,N'-dimethylhydrazine is used instead ofN-methylhydrazine.

We claim:
 1. A process for cleaving the amic acid function of a 7-(amicacid) cephalosporin having the formula ##STR11## in which R and R_(a)are hydrogen, or R and R_(a) taken together with the carbon atoms towhich they are attached represent orthophenylene;R₁ is a carboxyprotecting group; and R₂ is hydrogen, acetoxy, methoxy, methylthio,(5-methyl-1,3,4-thiadiazol-2-yl)thio, or(1-methyl-1H-tetrazol-5-yl)thio; which comprises
 1. contacting said7-(amic acid) cephalosporin with an alkyl chloroformate in the presenceof a tertiary amine to form the corresponding mixed anhydride having theformula ##STR12## in which R_(b) is an alkyl group having from 1 to 4carbon atoms;
 2. contacting the product mixture from step (1) with ahydrazine of the formula

    R.sub.3 HNNHR.sub.4

in which R₃ and R₄ independently are hydrogen or methyl; and 3.contacting the reaction mixture from step (2) with an acyl halide toproduce the corresponding 7-acylamido cephalosporin, said acyl halidehaving the formula

    R.sub.X -Y

in which Y is halogen and R_(X) is C₁ to C₈ -alkanoyl; C₂ to C₈ -chloro-or bromoalkanoyl; azidoacetyl; cyanoacetyl; 2-sydnone-3-C₁ to C₃-alkanoyl; ##STR13## in which m is zero, 1, or 2; ##STR14## in whicheach Q is hydrogen or methyl, and Ar is 2-thienyl, 3-thienyl, 2-furyl,3-furyl, 2-pyrrolyl, 3-pyrrolyl, phenyl, or phenyl substituted withchlorine, bromine, iodine, fluorine, trifluoromethyl, hydroxy, C₁ to C₃-alkyl, C₁ to C₃ -alkyloxy, cyano, or nitro; Ar--X--CH₂ --C(O)-- inwhich X is oxygen or sulfur, and Ar is as defined above; or Ar is4-pyridyl and X is sulfur; or ##STR15## in which Ar is as defined above,and B is -NH₂ ; an amino group protected with benzyloxycarbonyl, C₁ toC₄ -alkoxycarbonyl, cyclopentyloxycarbonyl, cyclohexyloxycarbonyl,benzhydryloxycarbonyl, triphenylmethyl, 2,2,2-trichloroethoxycarbonyl,##STR16## or the enamine from methyl acetoacetate or acetylacetone;--OH, or --OH protected by esterification with a C₁ to C₆ -alkanoicacid; --COOH, or --COOH protected by esterification with a C₁ to C₆-alkanol; --N₃ ; --CN; or --C(O)NH₂.
 2. Process of claim 1, in which theamic acid cephalosporin is reacted with an alkyl chloroformate in thepresence of a tertiary amine at a temperature of from about -20° C. toabout +5° C.
 3. Process of claim 2, in which the alkyl chloroformate isethyl chloroformate.
 4. Process of claim 1, in which R₁ is C₁ -C₄ alkyl,2,2,2-trichloroethyl, benzyl, p-nitrobenzyl, p-methoxybenzyl,benzhydryl, C₂ -C₆ alkanoyloxymethyl, phenacyl, or p-halophenacyl. 5.Process of claim 1, in which R and R_(a) are hydrogen.
 6. Process ofclaim 1, in which R and R_(a) taken together with the carbon atoms towhich they are attached represent ortho-phenylene ring.
 7. Process ofclaim 1, in which R₁ is p-nitrobenzyl.
 8. Process of claim 1, in whichR₂ is hydrogen.
 9. Process of claim 1, in which R₂ is acetoxy. 10.Process of claim 1, in which R₂ is (5-methyl-1,3,4-thiadiazo-2-yl)thio.11. Process of claim 1, in which R₂ is (1-methyl-1H-tetrazol-5-yl)thio.